Monday, April 28, 2014

Across the eastern half of the US, the bats you see in the
night skies this spring and summer have dramatically changed from the ones you saw
less than a decade ago.The little
brown bat, the once common dusk-time companion that harmlessly fluttered in millions
over American homes has undergone a 91% decline.Other species, like the endangered Indiana bat, have now
gone from modest steps toward recovery back to the doorstep of extinction.

The culprit is a disease, white-nose syndrome.First documented in New York in 2006,
over the short span of seven years the disease has been spreading south and
west across the US, reaching 25 US states and 5 Canadian provinces and already killing more than 5.7 million bats according to the U.S. Fish and Wildlife Service.

The disease is caused by a fungus
that was introduced and now resides within infected caves where it is acquired
when the bats enter for the winter.And because bats roost communally in caves, they often are all exposed
once the disease arrives.The
disease itself, in addition to causing the tell-tale white-nose on infected
bats, causes damage to wings and reduction in overwinter energy stores.The end result is massive (often over
90%) overwinter mortality in bat populations in infected caves within as little
as a single year.

But what about the half of North American bat species that are non-cave roosters?These
species that overwinter in trees or attics or migrate south for the winter and
otherwise avoid caves have yet to be found carrying the disease.Are these non-cave roosters
taking advantage of the night skies that formerly were dominated by little
brown bats and other cave-roosting species?

Rather than a free-for-all, researchers have already shown
that the night skies are highly structured and that bats typically avoid other
bats while out foraging.Bats tend
to feed in other areas or become active at different times in the evening to
avoid competition and interfering with each other’s echolocation calls (termed
acoustical jamming).For example,
little brown bats like to swarm around wetlands and to be active at dusk,
eating mayflies and other small, often soft-bodied insects; big browns forage
deeper in the forest on harder-shelled beetles and moths.Each bat species in the night skies has
a unique set of adaptations allowing it to exploit a separate potential niche. To see this you only have to open your
field guide so you can you can see the different wing morphologies that allow
the bats to forage in different ways, similar to the design of aircraft wings,
some ideal for maneuvering dense forests while others ideal for speed in open
wetlands.

I recently worked with researchers at Virginia Tech, U.S.
Forest Service and Ft. Drum Military Installation in New York where they have
been monitoring bats for over a decade to address the question:What happens when the cave-roosting
species die off and competition for space in the night skies of New York has
gone away? Results from our
investigations, soon to be published in the journal, Diversity and Distributions reveal that following the arrival of the disease and crash in formerly dominant
little brown bat populations, remnant bats primarily composed of non-cave
roosters were shifting their activity to the early evening hours.Also, several bat species were more
active in the wetland areas formerly dominated by little brown bats.It was evident that a massive re-shifting
of bats was occurring in the night skies of a post-white-nose syndrome world.

However, despite the passage of over 5 years since arrival
of the disease, we are not seeing more non-cave roosters on the landscape than
prior to the disease arriving.The
non-cave roosters have not yet translated the behavioral shift in using areas where
resources are likely more plentiful into higher survival and reproductive success.So the non-impacted, non-cave roosting
bat species are shifting when and where they are active, but so far they are
not responding in sufficient numbers to have the same impact that the
cave-roosters were having on the landscape.This means that millions of insects will no longer be
consumed, ranging from moths to garden pests and mosquitos.

Perhaps more troublesome, the non-cave roosting, often
migratory bats are increasingly threatened by their own set of factors,
including a recent push for wind energy development.These non-cave roosters have to make long seasonal movements
north and south to avoid the cold and take advantage of the summer insect
bonanza like so many migratory birds.But with increases in wind turbine development on their migratory paths,
we could be seeing a wicked problem emerging: disease is nearly extirpating cave-roosting
bats, and energy development is knocking back the migratory non-cave roosters.The end result is a dramatic decline and
uncertain future for bats in the night skies of North America.